1. Field of the Invention
The present invention relates to a method and to an apparatus for setting the paint throughput quantity of a motor-driven throughput control valve of a paint spraygun, particularly an automatic paint spraygun having a frequent change of throughput quantity and paint, preferably for assemblyline spraying of automobile bodies.
2. Description of the Prior Art
Given modern paint sprayer devices and systems, mechanical or electrical throughput regulating units which must be manually set are employed for setting the throughput quantity. The respective actual value of the throughput is thereby displayed by an independent measuring device and the operator then carries out a correction on the basis of the value that has been read. In complicated enameling or lacquering operations, for example when enameling automobile bodies, these known methods or, respectively, apparatus for setting the throughput quantity are, however, unsatisfactory. Therefore, for example, an automobile body comprises a plurality of spraying zones, i.e. zones having different intensities of paint application. When, for example, one proceeds on the assumption that the body is conducted through the painting station with an assembly line speed of five meters per minute, then the workpiece already traverses a distance of 8 cm in one second. The lengths of the spraying zones thereby lie between about 30 cm and 100 cm. In order, then, for a change of the throughput quantity for the paint sprayguns of the individual spraying zones to take full effect, the setting of the throughput quantity must occur very quickly, i.e. the transition from the maximum to the minimum throughput quantity should be possible within one section. This, however, is not possible with the known devices because both the actual adjustment times as well as the times for measuring and reading the actual values lie on the order of several seconds. When a change of paint or paint color is to be carried out between two workpieces, then a rinse operation requiring a fully-opened throughput valve must be carried out. Subsequently, the valve must be set to the throughput quantity of the first spraying zone of the following workpiece. Considerable time delays thereby occur precisely when changing paints or colors. Also to be taken into consideration is that the throughput quantity of the respective paint is dependent on the viscosity of the paint and, therefore, on the ambient temperature as well, with the consequence that the setting values change during a production stage. At any rate, the problems lead to the fact that the setting of the required throughput quantities is not only laborious and time-consuming, but also that deviations of 20% and far more must necessarily be accepted.